1. Field of the Invention
This invention relates to tape transports, and more particularly, to magnetic tape cartridge transport for transporting magnetic tape enclosed in a cartridge.
2. Description of the Prior Art
One of the most important requirements for a tape cartridge transport is that it include means for precisely aligning or registering the cartridge with magnetic recording and playback heads which are rigidly mounted on the transport. The transport must also accurately align the cartridge with the transport drive roller which provides a source of rotary motion for transporting the tape within the cartridge.
Magnetic tape cartridges used with digital computer processing equipment include a single registration tab on each of the lower front portions of each of the side edges of the cartridge. The registration of the cartridge upon the tape transport has typically been accomplished by providing a pair of over-center latches which rotate up into a locked position when a tape cartridge is fully inserted into the transport. These over-center latches rotate rearward out of the locked position when the cartridge is removed.
Over-center latches significantly increase the cost and complexity of the tape transport since they require a number of springs, spring attachment points and mounting hardware. Because of the friction forces between the over-center latches and the registration tabs during removal and insertion of the tape cartridge, the relatively soft aluminum registration tabs are worn and eroded. After a period of time erosion of the registration tabs requires that the cartridge be retired from service.
A further disadvantage of over-center latches is that proper registration of a tape cartridge in the tape transport is partially dependent on the manner of insertion of the cartridge into the transport by the user. Sloppy or nonstandard insertion techniques yield improper registration of the cartridge in the transport which can lead to degraded performance.
Magnetic tape cartridges of the type used in digital data applications include a belt capstan which must be frictionally engaged with an electric motor-driven tape drive roller to impart motion to the tape within the cartridge. Prior art magnetic tape cartridge transports pivotally mount the tape drive assembly on a lever arm which is spring biased into a predetermined position so that insertion of the tape cartridge forces the tape cartridge belt capstan into frictional contact with the tape drive roller with about a 14 ounce force. This force ensures proper frictional coupling of the drive roller with the belt capstan and guarantees that the rotary motion necessary to transport the tape in the cartridge is available.
Prior art tape transports also include a tape drive assembly which incorporates an electric motor for rotating a tape drive roller. This tape drive assembly consists of a pivotable, spring biased lever arm assembly to which the tape drive roller and motor are mounted. This assembly is spring biased to provide a 10 - 14 ounce force between the drive roller and cartridge belt capstan when a cartridge is fully inserted into the transport.
This prior art pivoted, spring biased assembly increases the difficulty of inserting the tape cartridge into the tape transport since during the final cartridge insertion movement, the relatively heavy tape drive assembly must be forceably displaced a distance sufficient to ensure proper spring biasing between the tape drive roller and cartridge belt capstan.
This tape drive assembly yields differing drive rollerbelt capstan pressures when the transport is mounted in a vertical position, as contrasted with a horizontal position. In a vertical mounting position the weight of the motor and its associated lever arm is the tape drive assembly is either added to or subtracted from the desired force between the drive roller and the belt capstan since the weight of the tape drive assembly would either add to or subtract from the spring biasing force which was designed into the system.
An additional disadvantage of this tape drive assembly is that it substantially increases the cost and complexity of the magnetic tape cartridge transport since a variety of mechanical attachment points, bearings, lever arms and springs are required.